Disease-Specific Associations of Physical Activity in Patients with Rheumatoid Arthritis and Systemic Lupus Erythematosus.

INTRODUCTION: Patients with inflammatory rheumatic diseases exhibit reduced physical activity (PA), contributing to increased cardiovascular risk and functional decline. While PA is recommended in both rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE), variables associated with PA remain poorly understood. Therefore, this study explored shared and disease-specific associations with PA in RA and SLE. METHODS: In this cross-sectional study, patients with RA (n = 200) and 94 SLE (n = 94), fulfilling ACR classification criteria, were recruited from the rheumatological outpatient clinic of the University Hospital Leipzig. Sociodemographic data were obtained from electronic records. Patient-reported outcome measures assessed comorbidities, PA and health-related quality of life. PA was quantified using the International Physical Activity Questionnaire Long Form. Associations were examined using multivariable logistic regression models. RESULTS: Patients with RA showed lower physical performance (p < 0.001) but higher PA levels than SLE (p < 0.001). In RA, fibromyalgia remained the only statistically significant variable and was associated with lower PA (OR = 0.001, 95 % CI <0.001-0.289; p = 0.017). In SLE, no independent predictors were identified; fibromyalgia (OR = 0.374, p = 0.209) and depressive symptoms (OR = 0.341, p = 0.063) showed non-significant trends. Self-reported PA and objective walking performance were moderately associated in both groups (RA: R² = 0.19; SLE: R² = 0.12). CONCLUSION: Associations with PA differ between RA and SLE. In RA, fibromyalgia is associated with lower PA, whereas in SLE, PA reflects a multifactorial interplay of functional and psychological factors, supporting disease-specific approaches to PA promotion.